Insulin resistance, also known as impaired insulin sensitivity, happens when cells in your muscles, fat and liver don't respond as they are immune to the cells.
Insulin is normally secreted by the beta cells (a type of islet cell) of the pancreas. The stimulus for insulin secretion is a high blood glucose.. Although there is always a low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Usually healthy body maintains it at 90mg/dl.
When people eat food the food breaks down into sugars which is only stored with the help of insulin. if insulin is not produced adequately then it is stored in the blood stream rising a person's blood glucose levels.
It takes few years or upto 1 year to develop type1 diabetes